Misc Electronic Questions

[kubeek]

Really, have you ever had like fractions and stuff at school? 6:1 means just that, 6 volts on input, one volt on output; or 24V input 4V output; or 1V input 0.1666V output. Or 6 gazillion volts input one gazillion volt output.
6:1 is the same thing as 1:1/6 or 1:0.16666
6:2 is the same as 3:1. You are free to call it anything you want as long as the ratio is the same.
6:3 is the same as 2:1 or 100:50 or 2000:1000 or 666:333. ditto

 

[Billy Mayo]

But would 6:3 be when a transformer has 3 isolated coils on the secondary winding? the 3 means how many isolated coils is on the secondary winding?

If a transformer has 3 isolated outputs on the secondary, would it change the ratio?

 

[KeepItSimpleStupid]

Each secondary can have their own ratio. Even a 6:1 ratio like your 150 V: 25V example won't work at 600 V to 1 volt even though they have the same ratio. You just can't apply 600 VAC to the primary of that transformer. The magnetics won;t support it.

Impeadance transformers are usually specified as say 600 ohm :600 ohm. Power transformers need more info: e.g. 120/240 or 120 x 120 for primaries. Both are different configurations.

A secondary might also be 4 x 35 V 3 A. I specified a xformer that I wanted made as 120 60 Hz Primary and 4 X 35 V 3A secondary. So, I got four bifilar wound windings at 35 V, 3A each on a toroidal transformer.

I probably could have actually specified what VA I wanted, but in the end I should have chosen a higher amperage. I didn't understand the concepts I needed at the time.

 

[Billy Mayo]

I have seen a transformer , 120 AC input on primary and the secondary had two coils, one at 24 VAC the other coil was 9 VAC

120 / 24 , ratio is 5:1

1 volt / 24 volts = 0.0416 volts

120 / 9 , ratio is 13.3 :1

1 volt / 9 is 0.1111

 

[Billy Mayo]

When their is a surge , swells, or spikes , how high can they go, normal is 120 VAC , what do they go up to?

Because at work a lot of transformers primaries are open or shorted because of surges, swelling and spikes

 

[KeepItSimpleStupid]

Remember it's usually expressed as primary/secondary. The primary is usually wound closer to the core, but transformer s WILL work both ways, so 0.416 is invalid. I'll also bet that in your 1:24 example it may be 24:1, but I don;t know which one is the primary.

Ratio is typically a ratio of whole numbers, not fractions.

 

[KeepItSimpleStupid]

Surges are all over the map, but let's say you were building an amplifier with +-50 VDC rails. You would rate components at 2x the supply voltage usually.

This isn't necessarily true for a 5V system.

 

[Billy Mayo]

The primary is the 120 VAC

Secondary coil#1 is 24 VAC
Secondary coil#2 is 9 VAC

How do you get the ratio and voltages?

 

[KeepItSimpleStupid]

There are two: 120/24 and 120/9; do the other math like: 120/9 = 40/1. Use ratios whe they are important. They usually are not.

 

[Billy Mayo]

120 / 24 , ratio is 5:1

1 volt / 5 ratio = 0.2

So for every 1 volt on the primary you will get .02 volts on the secondary from this 5:1 ration transformer?

120 / 9 , ratio is 13.3 :1

1 volt / 13.3 ratio

So for every 1 volt on the primary , you will get 0.075 volts on the secondary for this 13.3:1 ratio transformer?

 

[KeepItSimpleStupid]

NO! Ratios are express as whole numbers. 120/9 = 4/3 or 4:3

Your calculations are correct, but ratios are just that Ratios of Whole Numbers. An early math concept.

0.5/0.3 is a Quotient. 1/3 is a ratio

1 part of detergent to 5 parts water.

% is a concentration. Like (1/5*100) % of detergent. (you to the math)

0.5 can be a % in decimal, or 50% in percent units.

Early Math concepts. see: https://www.wolframalpha.com/input/?i=ratio

 

[Billy Mayo]

Visually Inspecting logic signals on a logic analyzer
This is what I have done
a. The Pulse Width was correct for each logic signal and logic channel
b. Time intervals apart from each pulse were correct and in sync with other logical signals
c. Leading and Falling Edges were sharp and not rounded or slanted

What other measurements can I do or what to look for?

When troubleshooting Analog or Digital circuits, What frequency and waveform do you set the function generator at mostly?

I set my up for sine waveform at 1Khz when injecting a function generator signal into a component to make sure its working right.

Using a Square waveform at 1Khz is better for troubleshooting , because if the square waveform has rounded edges or is slanted top or bottom , leading edge and falling edges are skewed , than it's a bad capacitor

What do you use a square waveform on the function generator for when troubleshooting using a square waveform?

 

[Billy Mayo]

Is there any way to measure the transistors .7 volts across the base to emitter , when the transistor is in circuit?

Because mostly the transistor is "energized" and past the turn on/forward biased voltage

So there is no way for me to measure the .7 volts right across the base to emitter?

Is energized a good work to use when saying it's been forward biased and turned on?

Also my manager said that you can't measure the .7 volts when a transistor is PNP because it's only .7 volts from base to emitter using NPN transistors, is that right?

 

[KeepItSimpleStupid]

"in circuit" always depends because of the surrounding circuitry. I won't say "always yes" or "sometimes". In general, you can.

The correct word to use when a transistor is "turned on", is indeed "turned on", or "in saturation". There is a spec called "Vce (Sat)". It's generally the lowest voltage drop you can get across the CE junction. "forward biased" would mean some amount of conduction, but not necessarily fully on. At least, that's my interpretation. It would mean, you could measure a Vbe across an NPN transistor with a voltmeter in circuit.

PNP's and NPN's just have their polarities reversed, so ~0.7 V across a BE junction of an NPN transistor makes sense, but so does a 0.7 V across the EB junction for a PNP makes sense. Just look at the schematic and follow the arrows. The arrow can be assumed to be the arrow of a diode.

 

[Billy Mayo]

Thanks for you information

Yes true, but why would a designer use a PNP transistor if it does the same thing as a NPN?

What have you seen PNP transistors used for

For me I have seen this:
1.) to invert a positive DC voltage INPUT on the base to a negative DC voltage OUTPUT on the collector
2.) to invert a HIGH logic to a Low Logic

I know i have seen PNP transistors in a push pull output stage

But I have seen PNP transistors used a inverters or when used as a Negative logic switch?

 

[KeepItSimpleStupid]

NPN transistors have an IC structure that's more superior to the PNP. The NPN was the first. A designer should generally choose an NPN if at all possible.

 

[Billy Mayo]

NPN transistors have an IC structure that's more superior to the PNP

What u mean by an NPN transistor has an IC structure more superior?


Here are 2 pictures of O-scope probes using a far reach measurement

Oscilloscope probe with ez hook to ground to get a far reach measurement causes NOISE why?


Oscilloscope probe with ez hook on the probe to get a far reach measurement cause NO noise

 

[Billy Mayo]

Here is some switch power supply waveform's

What kind of switching power supply waveform's is this called?

 

[KeepItSimpleStupid]

NPN v PNP: http://www.madsci.org/posts/archives/2003-05/1051807147.Ph.r.html

Noise: What's your best guess. It's obvious to me.

Two things to keep in in mind:
To Eliminate RFI: Shield
To Eliminate EMI: twist

Close parallel conductors radiate to each other. They inductively couple. Loops are also bad: http://en.wikipedia.org/wiki/Loop_antenna

Signal: Ringing See: http://en.wikipedia.org/wiki/Ringing_(signal)

Noise: You might consider making up a little adapter using some RG174 coax cable. Not really sure how it might work, but it might be worth a try. Get a BNC-M to BNC=F project box from Pomona and wire your scope probe straight thru. Also place a banana jack on the box. Put a length of RG174 coming out of the box thru a grommet. At the far end cut off the shield and heat shrink it and connect the center to an EZ-hook. Connect the shield conductor of the RG174 to the isolated banana plug. Connect the center conductor of the RG174 to the scope BNC ground.

Connect the banana jack to CHASSIS ground.

You will effectively have a shielded ground probe which should help. RFI, not EMI immune.

 

[Billy Mayo]

The Yellow EZ hook is not shielded?

The PNP has to much mobility and can't switch fast enough to be used as a switch

PNP have temperature problems more voltage drifting and voltage fluctuating i have notice , how about u?